Merge #1149: Remove usage of CHECK from non-test file

6a965b6 Remove usage of CHECK from non-test file (Tobin C. Harding)

Pull request description:

  Currently CHECK is used only in test and bench mark files except for one usage in `ecmult_impl.h`.

  We would like to move the definition of CHECK out of `util.h` so that `util.h` no longer has a hard dependency on `stdio.h`.

  Done as part of an effort to allow secp256k1 to be compiled to WASM as part of `rust-secp256k1`.

  ### Note to reviewers

  Please review carefully, I don't actually know if this patch is correct. Done while working on #1095. I'm happy to make any changes both in concept and execution - I'm super rusty at C programming.

  cc real-or-random

ACKs for top commit:
  sipa:
    utACK 6a965b6
  real-or-random:
    utACK 6a965b6

Tree-SHA512: 6bfb456bdb92a831acd3bc202607e80f6d0a194d6b2cf745c8eceb12ba675d03a319d6d105332b0cbca474e443969295e5a8e938635453e21e057d0ee597440b

Author: real-or-random

src/ecmult_impl.h

@@ -200,9 +200,15 @@ static int secp256k1_ecmult_wnaf(int *wnaf, int len, const secp256k1_scalar *a,
         bit += now;
     }
 #ifdef VERIFY
-    CHECK(carry == 0);
-    while (bit < 256) {
-        CHECK(secp256k1_scalar_get_bits(&s, bit++, 1) == 0);
+    {
+        int verify_bit = bit;
+
+        VERIFY_CHECK(carry == 0);
+
+        while (verify_bit < 256) {
+            VERIFY_CHECK(secp256k1_scalar_get_bits(&s, verify_bit, 1) == 0);
+            verify_bit++;
+        }
     }
 #endif
     return last_set_bit + 1;